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NIL values and variable initialization

Distinguishes missing values from zero and empty strings.

NIL values and variable initializationAdvPL

01 · OVERVIEW

Overview

Nil has ValType U; zero is N, empty string C and .F. L. Initialization should match the intended contract rather than replacing absence with apparent success. Check content/ranges after type validation. The example uses declared xValue initialized with Nil, not an unknown variable name. This distinguishes undefined value from an unresolved-name error. (Sources: refs. 1–1.)

03 · PRACTICAL EXAMPLE

Commented example

#Include "Protheus.ch"

User Function Ed705()
    Local xValue := Nil
    // U differs from zero, empty text and false.
    ConOut(ValType(xValue))
    xValue := 0
    ConOut(ValType(xValue))
Return Nil

Expected result

Displays U and N. Under review: editorial example neither compiled nor run in Protheus. Check includes, release, RDD and context before testing.

BEST PRACTICES

Do not index arrays or access methods before validating result existence/shape.
Under review: editorial example neither compiled nor run in Protheus. Check includes, release, RDD and context before testing.

NIL values and variable initialization

Overview

Commented example

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